The present invention relates to an apparatus for crushing material such as rock, ore, coal, stone and the like. This results in material of reduced size that can be stored or further processed. The apparatus for crushing material has particular application to the crushing of rock and ore in mining applications, however the invention is not limited to such applications and is suitable for crushing a variety of materials of the type mentioned above for different applications.
Smooth roll crushing is a technique of using an apparatus that includes two opposed rolls with a defined gap between them for crushing material. Each roll has a circular cross-section and extends longitudinally to form a cylindrical shape. The cylindrical crushing surface of each roll is usually smooth, but it is also possible for beads of welded material to be adhered to the crushing surface. In operation, an external power source drives each roll to counter-rotate, that is, one roll rotates clockwise and the other roll rotates counter-clockwise, and chunks of the material to be crushed are fed to the nip leading to the gap between the two rolls. The rotation of the rolls applies large pressures to the chunks of material in contact with the crushing surfaces, which causes the material to undergo internal stresses and fragment. Only fragments that are smaller in size than the gap defined between the rolls will pass through that gap allowing desired sized material to be obtained.
Smooth roll crushing is usually used when fine sized material is required as it is not usually suitable to process large size chunks of material. That is, smooth roll crushing generally requires quite massive rolls operating at high speeds to handle large sized chunks of feed material. Usually a size reduction of the material being crushed of only about 3:1 can be achieved. A problem exists that to increase the feed size, a large increase in diameter of the rolls is required, causing an increase in corresponding roll weight and torque requirements.
The discussion of the background to the invention herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge in this field in Australia as at the priority date of the present application.
The present invention provides an apparatus for crushing materials including
two rolls which are mounted in parallel to define a gap therebetween whereby surfaces of the rolls define a nip leading to the gap, the rolls being counter-rotatable for crushing material in the nip,
wherein each roll is similar and includes a longitudinally extending step provided by an outwardly extending face, each roll having a smoothly curved surface between the outer extremity of the face and the inner extremity of the face,
and wherein the rolls are located such that upon counter-rotation at the same speed the gap therebetween is maintained substantially constant and transversely reciprocates in location between limits defined by the outer extremity of the face of the step on one roll being located opposite the inner extremity of the face of the step on the opposite roll.
It has been found that an apparatus for crushing material according to the present invention can crush large size chunks of hard material using smaller diameter rolls and lighter weight machinery at lower speeds than known smooth rolls. This results in less expensive equipment, at lower weights and size that is easier to handle and locate. Furthermore, for a given size of feed material, the invention gives an increased reduction ratio in the size of the material being crushed compared to prior art smooth rolls of the same size.
Preferably each roll includes at least two steps, wherein each roll has smoothly curved surface segments which extend between the outer extremity of the face of one step to the inner extremity of the face of a following step.
Thus each roll may have only one step, although preferably they each have at least two steps in their crushing surfaces. Ideally each roll will have four steps, although any other number of steps is possible consistent with operational requirements and limitations.
Preferably each step extends longitudinally for the whole length of a roll.
Preferably each roll includes substantially equally peripherally spaced steps.
Preferably each smoothly curved surface segment is defined, in a cross-section of the rolls, by an arc of constant radius whose centre of curvature is offset from the centre of the roll. Preferably all radii of such arcs have the same magnitude, and all arc centres are offset equally from the centre of the roll and are equally spaced radially.
In at least one embodiment of the present invention, the face of the or each step is aligned along a radius of the roll and thus the inner and outer extremities of the or each face are also aligned along the same radius. Alternatively the outwardly extending face of a step may be substantially perpendicular to the adjacent surface segments whereby the inner and outer extremities of a face of a step may not be exactly aligned along a radius of the roll. Otherwise the invention encompasses other angles for the face of a step relative to adjacent surface segments so long as a step is thereby provided.
Each roll of the invention may comprise a generally cylindrical core on which are mounted shell segments that provide the longitudinally extending step or steps and smoothly curved surface segments therebetween. Preferably each such shell segment provides each surface segment and a step is provided by adjacent shell segments. For the mounting of such shell segments on a core, each shell segment may include a protrusion and each core include complementary shaped recesses so that a shell segment can be mounted on the core by sliding the protrusion thereof into a complementary shaped recess longitudinally of the core, whereby each protrusion/recess is shaped to prevent movement of a shell segment radially of the core. Preferably at least two protrusions are provided per shell segment.
In apparatus of the invention at least one of the rolls may be resiliently biased towards the other roll whereby for excess build-up of forces within the nip, said one roll is movable against the bias away from the other roll.
For a better understanding of the present invention and to show how it may be carried into effect, embodiments thereof will now be described by way of non-limiting example only, with reference to the accompanying drawings.